This invention relates to the gasification of carbonaceous materials. More particularly, the invention relates to the conversion of a solid carbonaceous fuel into gaseous products having increased fuel value.
Three basic processes have been developed for the gasification of carbonaceous materials such as coal. They are: (1) fixed-bed gasification, (2) fluidized-bed gasification, and (3) suspension or entrainment gasification. The present invention relates to the third type of process, suspension or entrainment gasification.
An inherent disadvantage of entrainment gasifiers is that they generate hot product gases. The heat must be recovered from the gases in order to utilize fully the heating value of the coal. It is known to quench partial oxidation gasification reactions directly in water or steam according to U.S. Pat. No. 2,957,387, U.S. Pat. No. 3,000,711 and U.S. Pat No. 3,723,345, or to partially cool the effluent gases by indirect heat exchange, as taught in U.S. Pat. No. 3,025,149. However, large amounts of high temperature heat are lost in quenching the effluent gases without enhancing the fuel value of the synthesis gas produced.
Another disadvantage of entrainment gasifiers is that they produce a substantial excess temperature in the gas product which requires quenching or cooling for subsequent heat recovery in conventional radiant heat water tube boilers. Thus, the product gas must be substantially cooled before it can be conducted to heat recovery boilers. As such, substantial quantities of otherwise useful high temperature heat are lost. Further, the capital investment for radiant heat boilers is quite high. Therefore, an alternative heat recovery boiler is an economic necessity for the entrainment gasifier processes.
A further disadvantage of entrainment gasifier processes is that sticky slag particles are carried through the partial gasification reactor and tend to foul the heat transfer surfaces of the heat recovery equipment.
Some of the reactions in a coal gasifier are exothermic and some are endothermic. A coal gasification process in which the heat generated by the exothermic reactions is used to provide the heat required for the endothermic reactions would be extremely desirable and energy efficient. Thus, it is an object of the present invention to provide an exothermic reactor partially oxidizing carbonaceous material with an oxygen-containing gas combined with a unfired second stage reactor to permit the endothermic reactions to proceed efficiently by reacting additional carbonaceous material with water, producing enhanced quality synthesis gas. This and other objects are accomplished in accordance with the present invention as described hereinbelow.